[Interest] Help parsing output of "mksquashfs" command

[Juan Navarro]

Hey Elvis, thank you for the tip. I'm convinced that this is the source of
the problem: the "output device" to which "mksquashfs" is writing, doesn't
show any number of "available columns" in my C++ code, thus it is probably
generating a progress bar of length 0. With a pseudo terminal as you
described, it will take the correct size and print a real progress bar.
Thanks! Also you made me have another look at the KDE Core libraries, which
will probably be of great help some day...

I'm not very fond though of introducing several extra dependency libraries
just to show progress in a small part of the application's purpose :-(
I think the better solution is convince the makers of this little tool to
make its output a bit more parseable.

@Michael: thanks for the tip, but I already checked that by redirecting
only stdout to a file in my initial tests, and saw how everything ended up
being written to the file, progress bar included.

On Fri, Jun 3, 2016 at 8:44 AM, Michael Sué <sue at sf.mpg.de> wrote:

> Hi,
>
>
>
> maybe the progress comes via stderr; you just catch stdout.
>
>
>
> - Michael.
>
>
>
> *From:* Interest [mailto:interest-bounces+sue=sf.mpg.de at qt-project.org] *On
> Behalf Of *Juan Navarro
> *Sent:* Thursday, June 2, 2016 1:47 PM
> *To:* interest at qt-project.org
> *Subject:* [Interest] Help parsing output of "mksquashfs" command
>
>
>
> Hello,
>
>
>
> I'm building a GUI tool under Kubuntu Linux 14.04, which among other
> things, creates SquashFS (https://en.wikipedia.org/wiki/SquashFS) images
> with the command-line command "mksquashfs". Due to the size of the images,
> this process takes a good amount of time, so I'd like to show its progress
> with a QProgressBar.
>
>
>
> Problem here is that the default output from this command is not really
> intended to be parsed. It uses a dynamic progress bar + a progress
> percentage which repaint themselves on the terminal, I guess that using the
> technique of printing "\r" (carriage returns) without "\n" (line feeds), so
> the progress bar is always drawn on the same row of the console output:
>
>
>
>     $ mksquashfs /home /tmp/test.sfs -noappend -processors 1
>
>     Parallel mksquashfs: Using 1 processor
>
>     Creating 4.0 filesystem on /tmp/test.sfs, block size 131072.
>
>     [======================================/                ]  699/1250
>  75%
>
>
>
>
>
> However I've found the way of printing the progress bar + percentage value
> in a serial way, ie. each iteration gets printed on its own line, with the
> following command line:
>
>
>
>     $ script --return --flush --quiet \
>
>     --command "mksquashfs /home \
>
>     /tmp/test.sfs -info -progress -noappend \
>
>     -processors 1" > test.txt
>
>
>
> With this, the output shown in "file.txt" is somewhat similar to this:
>
>
>
>     file ..., uncompressed size 2755336 bytes
>
>     [=========\                                             ]   481/12359
>   3%
>
>     file ..., uncompressed size 726904 bytes
>
>     [==========\                                            ]   528/12359
>   4%
>
>     file ..., uncompressed size 577 bytes
>
>     [==============\                                        ]   719/12359
>   5%
>
>
>
> This should be really easy to parse, extract the "x%" from the end of the
> line, and send that to the QProgressBar.
>
>
>
> So I've ported this command line to my Qt code. This is the relevant part
> of the code:
>
>
>
>     class MyClass
>
>     {
>
>         QProcess p;
>
>
>
>         void start() {
>
>             p.setProcessChannelMode(QProcess::SeparateChannels);
>
>             p.setReadChannel(QProcess::StandardOutput);
>
>             connect(&p, SIGNAL(readyReadStandardOutput()),
>
>                 this, SLOT(onProcessReadyReadStdout()));
>
>
>
>             QString c = "script";
>
>             QStringList a;
>
>             a << "--return" << "--flush" << "--quiet"
>
>             << "--command"
>
>             << "mksquashfs /media/data/KSHOW_320/RO/home "
>
>                "/tmp/test.sfs -info -progress "
>
>                "-noappend -no-recovery -processors 1";
>
>             p.start(c, a, QIODevice::ReadOnly | QIODevice::Unbuffered |
> QIODevice::Text);
>
>         }
>
>
>
>     private slots:
>
>         void onProcessReadyReadStdout() {
>
>             qDebug() << "New data:" << p.readAllStandardOutput();
>
>         }
>
>     }
>
>
>
>
>
> The problem is that given this code, the output doesn't contain the
> progress bar...
>
>
>
> With Qt 4.8.4:
>
>     New data: "
>
>     file ..., uncompressed size 2755336 bytes
>
>     "
>
>     New data: "
>
>     file ..., uncompressed size 726904 bytes
>
>     "
>
>     New data: "
>
>     file ..., uncompressed size 577 bytes
>
>     "
>
>
>
> With Qt 5.6.0:
>
>     New data: "\nfile ..., uncompressed size 2755336 bytes \n"
>
>     New data: "\nfile ..., uncompressed size 726904 bytes \n"
>
>     New data: "\nfile ..., uncompressed size 577 bytes \n"
>
>
>
> (Note how in Qt 5.6.0 the same command shows a different output, by
> explicitly showing '\n' characters; also the flag "QIODevice::Text" doesn't
> make a difference here).
>
>
>
> I'm quite lost here, because at this point I assume that QProcess is doing
> the right thing, but I don't understand at what point in the command chain
> the output is being generated differently between those two different ways
> of running the same command.
>
>
>
> It's probably the way the carriage returns are managed in the QProcess vs.
> shell redirection to a file, but I'd like to see if anyone here has some
> comment.
>
>
>
> Regards,
>
> Juan
>
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